


Secrets That Bind

by Lhugy_for_short



Category: Final Fantasy XV
Genre: Anal Sex, Blow Jobs, Bondage, Crownsguard Gladio, Enemies to Lovers, Falling In Love, Fluff and Smut, Hand Jobs, Hurrhurr, Inspired in part by Blood Bank, Kinda, M/M, Prince Prompto Argentum, Prince/Bodyguard AU, Spanking/whipping
Language: English
Status: Completed
Published: 2018-03-21
Updated: 2018-03-21
Packaged: 2019-04-05 13:28:26
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 4,201
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/14045253
Author URL: https://archiveofourown.org/users/Lhugy_for_short/pseuds/Lhugy_for_short
Summary: When Imperial Prince Argentum pays a visit to Insomnia under the guise of peace, no one is more suspicious than the very guard assigned to protect him. Gladio is certain Prompto is hiding something, and despite the risks he's determined to expose every last one of his secrets.





	Secrets That Bind

**Author's Note:**

  * For [Daiako (Achrya)](https://archiveofourown.org/users/Achrya/gifts).



> Heeey~  
> This is my submission for the Promptio-Off event between Raya (Daiako) and myself. The goal was to write a smutty Promptio prince/bodyguard AU + bondage in 5k or less, in an attempt to prove that the other one is a better writer. 
> 
> And also just an excuse to write more Promptio. Because UNF.

If anyone had bothered to ask for Gladio’s opinion - and they hadn’t - he would have told them that the whole damned city was getting worked up over nothing. The Empire that had nearly conquered all of Lucis was, at its core, after power, not peace. And allowing one of _their kind_ \- the Niflheim prince, of all people! - through the gates was only going to lead to disappointment and trouble in the end.

Gladio wasn’t the only member of the Crownsguard, the elite force charged with protecting King Regis and his son, to share such pessimistic opinions. But he _was_ the only one stupid enough to try to voice them to Cor. “Dissent” had seemed an awfully dramatic word to use just for questioning the motives of what was technically an enemy nation; but the Marshal was a stubborn man, and Gladio was going to lose that battle ten times out of ten. Not only did his complaining cost him his seat at the next annual Glaive’s cookout, but it also landed him with bodyguard duty for the duration of the peace talks.

For none other than the Niflheim prince himself.

It was already looking to be the longest week of his young career.

* * *

 

On the day Prince Argentum, adopted son of Iedolas Aldercapt and heir to the snowy Empire, arrived in Insomnia, the streets were filled with thousands of warm, smiling faces. Buildings were decorated in gaudy colors, streamers hung from balconies, and music played in a cacophony of celebration and sound - all to welcome the young man who, to the Lucian people, represented _progress_.

Prompto was in every way the opposite of his father. Where Iedolas was old, firm, stuck in his ways, the prince radiated kindness and compassion. Where the Emperor thought only of expanding his reach by any means necessary, Prompto was focused on rebuilding: helping refugees of the war his father had wrought; negotiating armistices that stopped the killing of innocents; and spoke out vocally against the violence.

It was easy, then, to see why the people of Insomnia loved him. On the outside, he was a perfect symbol of the peace they had dreamed of for so long. And yet to some, like Gladio, his apparent philanthropy did little but incite suspicion. Why, for instance, did Iedolas tolerate his son’s outspoken criticism? Why had he gone so far as to make him Niflheim’s official emissary, and send him on missions of peace, like this one to the Citadel?

No, something didn’t sit right about the whole situation. It stunk worse that a Dualhorn carcass in the middle of a Leiden summer, and Gladio was determined to spend the week getting to the bottom of it.

He waited, along with the rest of the Crownsguard, at the base of the Citadel’s steps. In the distance, he could see the prince’s white car - just the one, which seemed odd - making its way through the crowded downtown streets. As it drew closer, King Regis and his son, Noct, descended the stairs and waited to welcome their esteemed guest with open arms.

The car pulled up at the curb. The back door opened, and a lone figure stepped out, looking small against the backdrop of Insomnia. Gladio found himself leaning around several heads for a better view.

Prompto Argentum was smiling. A tiny, almost shy smile beneath smooth, freckled cheeks. His eyes were blue, startlingly so, and popped like jewels behind a curtain of light blond hair. Unlike the Glaives, the Crownsguard, and their King, the Niflheim prince wore robes of white and silver, practically glowing in the sunlight. If Gladio were a weak man - and he wasn’t - he might have been stunned speechless by the kid’s unexpected beauty.

But as it was, he was thankfully spared the embarrassment when Noctis Lucis Caelum dashed forward and pulled Prompto into a hug.

“Welcome, Prince Argentum, on this most honored occasion -- “ Whatever else Regis said was swallowed up in the cheers of the crowd. Gladio strained to listen, to watch, but before he knew what was happening, Prompto was moving again. Right up to the steps and nearly past him, until the sound of the Marshal’s voice cutting through the excitement halted the procession.

“Prince Argentum! Where is the rest of your security detail?”

Round, blue eyes blinked. Prompto scanned the faces of the Glaives for the source of the voice, and smiled. “Sir, I’m here for peace, not conflict. I didn’t think I needed any bodyguards.”

Gladio’s jaw nearly unhinged. _Was this kid serious? What kind of idiot waltzed into enemy territory without any sort of defense plan? Or, could it be possible that there was more than he was letting on to?_

A firm hand on his shoulder dispelled the thoughts. “Well, then,” Cor smirked darkly at his side. “Looks like Gladiolus will have his work cut out for him.”

* * *

 

“Thank you again for your hospitality, Your Highness.”

“Think nothing of it, my boy. Noct wouldn’t stand for anything less.” Regis chuckled as he gave Prompto’s shoulder a pat - a decidedly congenial gesture that served to further sour Gladio’s mood. “I’ve already asked some of my staff to deliver your bags up. Is there anything else I can do to make your stay more comfortable?”

Tufts of blond rustled as the prince shook his head. “No, you’ve already done so much for me,” he smiled, and Gladio thought he detected a hint of a shadow passing over those too-blue eyes. “Allowing me to stay under your own roof - Lucians really are as gracious of hosts as the stories say.”

At that, Regis ruffled the young prince’s hair. Smiled fondly as he bid him a good night’s rest on the eve of their peace talks. Then the King and his detail of Glaives turned back to the main hall, leaving Prompto alone with his assigned bodyguard - who, at that moment, was leaning against the entrance of the guest chamber and all but glowering.

For perhaps the first time since that afternoon, blue eyes rounded on him. Prompto curved his lips up thoughtfully. “And thank _you,_ as well, Mister…?”

“Gladio. Just Gladio.”

“Right, sorry. There’s been a lot to take in today. Usually I’m better with names.”

“It’s fine.” Pushing himself off the wall, Gladio kept his face a mask of disinterest as he approached the young prince. He watched as that blue gaze ook in his intimidating stature - the thick, corded muscles, the fierce cut of his jaw, the black lines of his tattoo visible around the sleeves of his uniform. And Gladio smirked at the way Prompto seemed to shrink before him. “You’re bold, kid. The King may have a soft spot for you, but don’t forget: you’re surrounded by enemies here. People who’d like to see you exposed for what you _really_ are. To come here without any guards to protect you….”

He reached out, merely to straighten the collar of Prompto’s robes, but the blond shuddered visibly under the touch. Out of fear? Guilt? Gladio couldn’t be sure, but he was more certain know than ever that this prince had something to hide.

“Mister Glaive….” Those blue eyes gazed up. Prompto looked as if he were about to say something; his lips parted and he sucked in a breath so close that Gladio could hear the way the air hitched in his throat.

But suddenly, a sound from behind him shattered the tension. Monica Elshett nodded to them both as he walked past carrying a heavy suitcase, followed by several more Citadel staff in similar fashion. With the moment temporarily forgotten, Prompto’s expression returned to its usual bright, cheerful state, and he trotted into the bedroom after his things.

“Ah, please leave that one over there. Could you put that one on the sofa? Thank you very much.” Gladio’s brows knotted upon entering the room. For someone who planned to stay only one week, The Niflheim prince had sure brought a lot of things with him. Suitcases, trunks, bags; all looked filled to the brim as they were arranged to his liking around the room. Prompto thanked the staff again as, their task finished, they bowed and retired for the night.

Only Gladio remained. The prince had yet to acknowledge his presence, and so he hung back to watch Prompto tear into the first suitcase, grin, and pull out....

...Clothes. Just clothes.

Gladio’s frustration deepened. While Prompto was busy laying his robes out over the back of the sofa, the dark-haired bodyguard slunk along the wall to the luggage piled by the door. Ran his fingers along the edge of one of the trunks and narrowed his eyes. Was just about to reach for the lock to reveal whatever dark secrets were stashed within - weapons, traps - when a sharp voice called out to him.

“Mister Glaive.” Gladio glanced over his shoulder to see Prompto standing rigid next to the sofa, face pale and eyes wide. “It’s late. You’re free to go home.”

A sneer. “I’m not a _Glaive_ , I’m in the Crownsguard. And I’ve been assigned to keep my eye on you day _and_ night. So relax, _Princess_ ,” he added gracelessly, and was rewarded when Prompto’s face flushed several shades of distressed. “Besides. I thought you could use a hand unpacking all these bags.”

“Not…. Not that one.” There was something in his voice, the way it broke, that had Gladio moving closer to the trunk in question. Now, without a doubt, he knew there must be something inside worth hiding; something the prince wanted so badly to keep secret that he was suddenly flying across the room to tug at Gladio’s wrist.

“Please,” those blue eyes begged, shining with fear. “Don’t.”  

Gladio knew he should call for backup, that he was taking a huge risk in an attempt to prove his hot-blooded theory. But he’d never been one to walk away from a challenge, especially not one in which the safety of the city hung in the balance. So he grabbed the Niflheim prince by the front of his robes and hauled him, gasping and struggling, over to the wall. Pushed him onto his knees and held him in place with rough fingers in his yellow hair.

“I’m onto you, you know. Everyone else here might buy the bullshit innocence act, but I see right through you.” Under his cruel grip, blue eyes hazed, and soft, pink lips quaked with every word. “Open the case.”

Slowly, Prompto leaned forward. Tears stung at his eyes as he opened the lock and tried, one last time, to beg for mercy. Gladio showed him none. Not until the trunk was open before him, and he was forced to release his grip on the prince in utter shock.

 _It was some secret, alright._ But rather than the knives or bombs or guns he’d been expecting, he found...sex toys. _Big_ ones. Along with straps and manacles; several whips of different lengths and hardness; black material which shined like rubber in the light, and creaked under Gladio’s hesitant touch. And that was just what he could see from the surface. _What in the name of the Six…?”_

Beside him, nearly forgotten, Prompto suddenly whined. “Please don’t tell anyone. I don’t know how you figured it out, but….” He paused, cheeks a dark red - in shame, not fear, Gladio now realized - and wiped the back of a trembling hand across his eyes. “I thought I’d been so careful. Please, Glaive, don’t tell Noctis.”

His heart was pounding in his chest. Gladio looked from the man at his feet to the suitcase, back again as his brain tried to wrap around what he was seeing. _This_ was the Niflheim prince’s big secret? That he liked to tie people up - or _be_ tied up, his mind inappropriately supplied - and get rough in bed? It would have been enough to make him laugh if his chest hadn’t been so tight.

“I won’t say anything to Noct,” he agreed in a flat voice once he managed to find it again. “Or anyone else.”

Blue eyes gazed up at him from beneath blond locks in reluctant hope. “Really?”

“Yeah. Just...explain one thing to me.”

“Anything.”

“What in Ifrit’s name were you planning to do bringing all this stuff here with you?”

The prince didn’t answer right away. He reached out to stroke his fingers along the curve of a wide-base, black silicon plug. Gladio’s throat went as dry as a desert. “I get...lonely. A week is a long time to wait, you know.”

Of course, Gladio was inclined to disagree, if only because all this stuff seemed a pain in the ass (no pun intended) to drag halfway around the world when the alternative was a few nights of celibacy. But what that implied about the blond, blushing prince, _well_.

Turned out the “innocence” really was an act.

Gladio had to force his eyes away from the sight of Prompto kneeling, thighs spread, on the carpet. He should have left him at that, no more questions, no more _curiosity_. The story should have ended there, an unspoken secret between a prince and his bodyguard. Yet, like most secrets, this one refused to be forgotten so easily.

“So, uh. Which one are you?”

Prompto blinked up, half in confusion, half in surprise that Gladio was still standing there. “Which one...what?”

An anxious shuffle of feet. The larger man cleared his throat. “You know. Are you the one who usually... _wears_ this stuff, or…?”

Another moment passed before Prompto gathered his meaning. He flushed, turned again to the trunk, and drew out a thin strip of black silk. It caught the light beautifully, spilled from his fingers like ink as he held it up for Gladio and passed it into his grasp. Time stopped along with the bodyguard’s breath. The prince chewed his lip as he answered, “Would you like me to show you?”

* * *

 

It was Gladio’s hands, in the end, that had done it for him. Being treated so roughly, talked down to by a guard ( _a guard, and him a prince!_ ), and those thick fingers in his hair - together they had started Prompto’s blood burning with need. Getting pushed around by this man - this big, tactless, fierce, _hairy_ man - was exactly how he wanted to spend the rest of his week in the Crown City.

“Mister Glaive?”

“ _Gladio,_ ” the rough voice reminded him from somewhere at his back. Not that he could see what was happening, of course; not with the silk covering his eyes, but he could feel the other man’s heat. Felt his burning gaze traveling over every inch of his body as he stood, naked and shivering, in the center of the room.

“Um. G-Gladio?”

“A puff of hot breath on his neck. “Yeah, Princess?”   

“A little tighter, please. I can still move my wrists.”

He felt Gladio approach again. Thick, calloused fingertips trailed over the curve of his shoulder, down the planes of his back where his shoulder blades drew together taut. Down further still to hook around the bonds that held his wrists fast, and tugged. “How much tighter?”

“Tight as you can.”

The final word left him in a gasp. Gladio pulled the ends of black silk until the fabric was digging into Prompto’s skin, yanking his arms back painfully.

But the pain, of course, was half the thrill.

“Better?”

The prince was already hard, embarrassingly so with his cock leaking where it jutted out in the chilled air. “B-better. Have you ever used a whip before?”

If Gladio noticed the trembling in his voice, he said nothing. “Can’t say that I have. You want me to whip you?”

“ _Yes._ ” Then, steadier: “T-the small one. Start with my thighs.”

There was a rustling from the bed while Gladio picked out his weapon of choice. Prompto could hear him testing the firmness of the leather in his grip, the delicious creak of it already making his pale skin flare red. A moment of tense anticipation, then at last the cool, emotionless stroke of the handle across his ass, the backs of his legs, had him squirming. “Yes, r-right there. Please.”

As expected, the first strike was tentative, little more than a pat of leath to delicate skin. But the second time --

“A- _ahh!”_

He’d been right in choosing this Glaive. Prompto cried out at the sharp sting of the whip as it cracked across both thighs. Left an angry welt in its place when he heard Gladio pull back, squeeze his grip, and strike again.

“ _Mmm!”_ The prince swayed dangerously where he stood. Blood rushed to the surface of his freckled skin, combined with the pleasure/pain that racked his body to throw him nearly off balance. A third strike, and even with the silk covering his eyes he sensed the room start to spin.

His bodyguard was there to catch him. Strong arms weaved around his waist, held him upright despite the way his legs had gone weak beneath him. “Gotcha, Princess,” Gladio said into his ear, and then Prompto was being lifted off the ground, hauled bodily across the room to be tossed - _tossed!_ \- onto the luxurious bed. He managed to roll onto his stomach just as the mattress sank down behind him under Gladio’s weight.

“More?”

Though it stung, the caress of the whip against the backs of his thighs left Prompto shivering. When he spoke, his voice was raw, strained, hardly like himself and yet -- “ _More.”_

Gladio flogged him until his ass and legs were a fiery red. By then, the prince was too much of a mess to speak - to even beg his bodyguard to stop - and his pretty cock throbbed heavy, painfully hard against the sheets. At last, Gladio took pity on him. Untied the prince’s wrists and rolled him onto his back. Slipped off the blindfold and cradles him, knees bent, and with his sweat-matted, blonde head in his lap. Curled thick fingers around his dick and stroked him until, before long, he was coming in weak bursts across his naked belly.

There was a potion in on of Prompto’s suitcases. Gladio cracked it open, fed half of the glowing liquid through trembling lips, and lathered the rest over soft, abused skin. Prompto hissed as the magic took hold - slowly released his breath. The tension drained from his face in time with the potion pulsing through his blood.

For several moments, Gladio watched him. _Prince Argentum_ , who had spent the entire day unintentionally working his way under usually thick skin. Who had, since that very morning, carried an air of intrigue and suspicion. _Prompto_ , who suddenly seemed so beautiful and so foreign, like uncharted territory that cried out to Gladio’s sense of adventure, his curiosity, impossible to deny.

Blue eyes slid open, and Prompto smiled to see his bodyguard still so close. “Thank you,” he whispered. Gladio couldn’t find an answer to that. Instead, he patted the prince on his shoulder and, in silence, pushed himself up from the bed as if he’d been dismissed.

A sudden hand tangling in the back of his shirt stopped him. If he’d been a stronger man - and he most certainly wasn’t - he would have bid the Niflheim prince good night and gone to take up his post in the hallway. But as it was, he turned to meet that stunning, pleading gaze. Let pale fingers work open his uniform and release his own neglected cock into the open air. Groaned as Prompto sucked him down, inch by inch, until he’d lost himself in the overwhelming heat of his expert mouth.

* * *

 

One week passed far too quickly. While at first Gladio had expected it to be boring, tedious, filled with council meetings and long nights of watch, the opposite couldn’t have been more true.

There were still meetings, of course, and work to be done, but each day held the promise of another night in Prompto’s bed at the end. The prince was, as Gladio had correctly suspected, _insatiable_ , and the youthful energy he exuding during the afternoon lasted until long after the sun had set again.

Not that Gladio was complaining. He’d begun to grow fond of the sight of pale skin reddening under his ministrations. Liked the way Prompto looked, sounded, _felt_ squeezing around him, bound and bouncing on his cock. He’d begun to enjoy the cool touch of leather sliding over his flesh from the contraptions and costumes the yellow-haired prince sometimes wore. The inky black, too, painting the perfect contrast on Prompto’s frame.

But the time had come for the negotiations to draw to a close. Regis had entrusted Prompto with several messages to take back to his father in Gralea, and had bid him make haste at first dawn’s light. Prompto, as was expected of him, bowed his head in understanding; across the room, meanwhile, a silent protest as Gladio clenched his fists.

His emotions were still surging when he followed the unusually quiet prince up to his room that night. The door slammed shut. Prompto stripped off his robes without a word, and moved immediately to help Gladio undress, as well. But firm hands caught his wrists, held him locked in place as hard, amber eyes reigned in cloudy blue.

“Stay.”

Prompto’s eyes widened. His lips quivered with surprise, with confusion. “You know I can’t.”

Neither of them were ready when Gladio pressed forward to claim him in a kiss. Neither quite understood what it meant, or the depths to which their week of harmless play had taken them. Yet neither did they know how to pull away. The kiss carried Prompto back, across the room until his thighs hit the edge of the mattress. Gladio continued forward, and together they fell onto the bed just as their lips broke for air.

“ _Stay,”_ the larger man said again.

Blue eyes swam, darkened. “ _I can’t._ ”

Next to the pillow was one of the black silk straps they had used the night before. Gladio reached for it, pinning Prompto’s naked body beneath him with his weight, kissed him again distractingly as he guided pale arms above his head. Lashed his wrists together and then to the headboard, the only sound besides the rustle of silk coming in the form of heavy breaths in the space between.

Though he didn’t speak, every touch, every press of lips to skin was like a plea. With each scrape of teeth over the curve of Prompto’s neck, he begged him not to leave. With every graze of fingernails along his chest, his hips, his thighs, he confessed the need in his heart. When he parted Prompto’s legs and buried his face in musky heat, it was a promise to remain at his side, a loyal bodyguard in the service of his beloved prince.

Prompto responded with a tentative promise of his own. Legs wrapped around broad hips, he drew Gladio down and into him. Moaned his name as he was lifted off the bed and into Gladio’s lap; arched and rolled onto his thick cock as if somehow, by taking his deeper, _deeper_ , they could remain together in spite of fate.

The prince kissed Gladio through both of their orgasms. Hung from his lips long after he’d been filled with slick release, and kept his legs locked to hold him in place until, at last, the night came to an end. The moon outside the palace windows set to the sight of dark fingers stroking back through golden hair, and lips brushing together in lieu of better words. _Stay,_ one pair seemed to say; _Come with me,_ begged the other. And they fell together again as darkness spread across the sky.

* * *

 

 

Gladio watched from the steps of the Citadel as Prince Argentum hugged the royal family goodbye. Despite his bright smile, there were tears clinging to the corners of his eyes, falling down his freckled cheeks to the sound of Noctis’ promise that they would meet again soon. No one else noticed that blue gaze flicker up to the line of black uniforms positioned on the steps, or the wistful smile he cast in the direction of a certain dark-haired guard.

No one else but Gladio.

His fingers tightened around the strap of black silk in his pocket - a favor gifted to him by the prince who had enchanted his heart in the course of a single week.

“I know we will,” he heard Prompto say in a voice just loud enough to reach him, and Gladio nodded his head in assurance.

Even after that white car had pulled away from the curb, his scent still lingered. The feel, the taste of his lips on Gladio’s mouth remained - as permanent as his tattoo or the scar on his face - while he watched the prince drive out of sight down the streets. Out of Insomnia, back to the snowy mountains of Niflheim to a palace halfway around the world. Leaving in his wake the hope for peace, for progress, and for a better future for both the Lucian Kingdom and the Empire.

As well as a secret. One which Gladio kept both in his heart and in his pocket, waiting for the day they would finally meet again.

 

**Author's Note:**

> There's not voting or judging in this event lol we just hope everyone enjoys the Promptio


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